Primary small cell neuroendocrine carcinoma of the breast.

We report and characterize immunohistochemically a case of primary small cell neuroendocrine carcinoma of the breast. The tumor, which arose in the left side, was 18 cm in maximum diameter and microscopically was composed of patternless sheets of undifferentiated small cells with a high nuclear-to-cytoplasmic ratio, hyperchromatic nuclei with indistinct cytoplasm, inconspicuous nucleoli, numerous mitotic figures and large areas of coagulative necrosis. Tumor cells were positive for bcl-2, neuron-specific enolase, synaptophysin, CAM 5.2 and cytokeratin AE1/3, but negative for LCA, CD30, HMB-45, chromogranin A, estrogen receptor, progesterone receptor, Her-2/neu and CD99. The opposite breast harboured an intraductal carcinoma with a focus suggesting microinfiltration, a finding never reported before. In this paper we have also extensively reviewed the literature on the subject, emphasizing the variable immunohistochemical profile and the aggressiveness of mammary small cell carcinoma. The rapidly fatal clinical course of our case, which appears to have the largest dimensions described in literature, underlines the importance of an early diagnosis and treatment for long-term survival.